Surface functionalization of pigments and/or dyes for radiation curable ink printing and coating applications

ABSTRACT

Functionalized pigment compositions produced by reacting a radiation reactive organ metallic coupling agent with a pigment/dye.

This is a 371 of PCT/US01/47241, filed Dec. 10, 2001 which is a CIP ofSer. No. 09/736,129, filed Dec. 15. 2000, now abandoned.

BACKGROUND OF INVENTION AND PRIOR ART

This invention relates to surface functionalization of pigments and/ordyes for radiation curable ink printing and coating applications.

In general, printing inks and coating materials can be classified infour categories: solvent-based, water-based, radiation-curable andpowder materials. The compatibility between pigments/dyes and organicresins (as coating matrix or printing vehicles) is one of the mostcrucial factors affecting not only processability but also performancein both coating and ink printing industries. Pigments/dyes that are usedin non-polar environments must be readily dispersible, and thereforehydrophobic. In contrast, pigments that are used in polar environmentsmust exhibit highly polar surface characteristics. In the extreme casesof water-borne inks or coatings, the degree of polarity may need to befully hydrophilic.

It is important to be able to render desired surface characteristicsthat can match the polarity of resins and diluents (solvents or water).Pigment/dye surface modification has been a challenge for a long time.

It is well known, for example, to use surfactants to improve thedispersibility of pigments, but the utility of such a process is usuallylimited. Short shelf life or relatively poor thermal stability of thepigment/dye dispersion is a main concern. An invention described in U.S.Pat. No. 5,808,118 relates to a surfactant consisting of the product ofthe simultaneous reaction of a sulfonic acid, a saturated fatty acid anda polyamine. The advantage of this invention is to provide betterdispersion stability.

Organic silanes and silicone oligomers have been extensively employed ascoupling agents in surface modification for various inorganic pigmentssuch as transition metal oxides (U.S. Pat. Nos. 6,120,596, 5,665,155,4,404,318, 5,719,206, 5,820,977, EP 0725115 WO 00/04421, WO 99/57204,etc.). Various hydrophobic groups were attached on the pigment surfacethrough covalent bonds. The major limitation of this method is that nocoupling reaction will take place between the organic silanes and thesurface of pigments/dyes if there are no hydroxyl groups on the surfaceof the pigments/dyes.

A method for making a non-polar suspension of charged pigment particlesis illustrated in WO 00/05313. In this method, a covalent bond is formedbetween the pigment and the surface modifying polymers which have one ofthe following groups: carboxyl, hydroxyl, anhydrido, amino, amido, halo,thiol, epoxy, keto, aldehydo, isocyanato, and alkenyl. Pigments can alsobe treated with nitrogen-containing copolymer of a variety ofpolyurethanes (U.S. Pat. No. 4,844,742).

Hydrophilic characteristics of pigment surface are provided in variousways. Organic pigments and transition metal containing pigments(hydrophobic) can be treated in phosphoric acid and/or its monoester(U.S. Pat. Nos. 5,865,885, 5,466,482 EP 0717085). Magnetic pigments canbe surface treated in one or more aralkylphosphonic acids (U.S. Pat. No.6,099,895). Pigments can be surface coated by mixing titanium oligomersand organic acid esters (EP 568720).

The mechanisms of chemical and physical adsorption are often used forpigment/dye surface treatments, although these types of links are not asstable as covalent bonds. Zinc oxide powder can be immersed in one ormore organic liquids selected from alcohols, ketones, amines and esters(U.S. Pat. No. 5,672,427). Pigments can also be treated with poly (vinylalkyl ether)s (EP 0500494)

In the U.S. Pat. No. 4,622,073, metal powder pigment is treated with anorganic titanate having the general formula: Ti(OR)₂[OC₂H₄N(C₂H₄OH)₂]₂wherein R is alkyl group of 1 to 8 carbon atoms. In the U.S. Pat. No.4,080,353, pigment is treated with titanate-phosphite adducts which arethe reaction products of (RO)₄Ti and di-substituted hydrogen phosphite(R′O)₂P(O)H where R and R′ are monovalent alkyl, alkenyl, aryl, aralkylor alkaryl.

Radiation (UV/electron beam) curable printing inks and coatings havebecome very well accepted technologies because their distinct advantagesincluding low or non VOC, fast process, high performance, etc. However,formulating ink and coating materials is a challenge because of the poorcompatibility between UV-resins and pigments/dyes, and therefore, poordispersibility and wetting ability. None of above citedliterature/patents has disclosed any method addressing this issue.

SUMMARY OF THE INVENTION

The present invention relates to a method to surface functionalize bothinorganic and organic pigments and dyes. In the functionalizationreactions, organic titanate and zirconate and aluminate compounds areemployed as coupling agents, more exactly, as a molecular bridge at theinterface between two dissimilar phases, such as inorganic/organic orimmiscible organic/organic phases.

The coupling agent is represented by the formula:(RO)_(m)-M-(O—X—R′—Y)_(n)where, M is a metal atom selected from the groups consisting of GroupIIa, IIIb, IVb, Vb, VIb, VIIb, VIII, Ib, IIb, and IIIa

and preferably, Ti, Zr, or Al,

RO is a hydrolyzable portion, or proton-bearing moiety and R is C₁ to C₈substituted or unsubstituted alkyl or hydrogen,

X is an organic functional group such as alkylates, carboxyl, sulfonyl,phenolic, phosphate, pyrophosphate, or phosphite etc.

R′ is an organic group such as C₂ to C₈ alkyl or substituted alkyl,which provides van der Waals' entanglement via long carbon chains for avariety of mechanical properties.

Y represents a radiation curable functional group, such as, but notlimited to acrylate, methacrylate epoxy, and vinyl as well as otherunsaturated groups, m varies from 1-3 and n is 1-3.

Depending upon the structure of the interface of the dissimilar phases,and also, upon the type of the coupling agents employed, the couplingmechanisms fall into one or more of the following categories:alcoholysis (condensation), surface chelation, coordination, ligandexchange, chemical adsorption.

In the present invention, surface functionalization of pigments/dyesprovides not only the desired surface characteristics to satisfy thecompatibility requirements for pigments/dyes and resin matrix, but alsoradiation (UV light or electron beam) reactivity. Therefore, the surfacefunctionalization provides the capability of co-polymerization betweenpigments/dyes and matrix resins in the later radiation cure process.

Suitable resins to be admixed with functionalized pigments includepowdered resins such as polyesters or epoxy resins.

Liquid monomers and oligomers such as acrylates, methacrylates, epoxiesor vinyls may also be admixed with the functionalized pigments/dyes andthen are subjected to radiation curing.

The functionalizing or coupling agents may first be added to the resins(oligomers, monomers or polymers), and pigments/dyes. Other additivesmay be added to the mixture later.

The amount of coupling agent is generally based on the reactivity ofcoupling agent, surface morphology of pigments/dyes as well as thedesired properties of the formulation such as the desired flow rate forinks, etc.

The present invention makes the dispersion/grinding process easier, andtherefore, reduces the process cost.

The present invention enhances the performance in either coatings orprinting inks in many aspects. The Theological behaviors of uncuredmaterials including melt powder-coating materials, pigmented coatingmaterials and inks are significantly improved. These improvementsdirectly result in the better coating and printing processability. Theperformance enhancements of cured pigmented coatings/inks may includesurface hardness, modulus, flexibility, elongation strength, adhesion tosubstrate, chemical and corrosion resistance. These enhancements andimprovements are believed to be the result of the high compatibilitybetween matrix resins and modified pigments/dyes. The surfacefunctionalization reactions provide a variety of radiation-curablefunctionalities, such as (meth) acrylate, epoxy etc, which are similarto, even the same as that of resin matrix. More essentially, theseenhancements and improvements are the result of the unique structure ofcured ink films/coatings, i.e. homogeneously distributed pigments/dyesthat are chemically bonded to resin matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 depict flow tests of inks employing the functionalizedpigments of the present invention vs. the control.

DETAILED DESCRIPTION OF INVENTION

Two examples are presented here to demonstrate that this invention canbe used in two completely different application areas.

EXAMPLE 1 Property Improvement for Radiation Curable Powder Coatings

Materials

-   1. UVECOAT 2000, a UV powder-coating resin produced by UCB Chemical    Corporation.-   2. Ti-Pure R-960, TiO₂ Pigment from Du Pont, was used as received.-   3. NZ-39, neopentyl(diallyl)oxy triacryl zirconate, a coupling agent    obtained from KenRich Petrochemicals Inc, was used as received.-   4. Reflow P-67, a flowing agent from Estron Chemical, was used as    received.-   5. Oxymelt A-4, a degassing agent from Estron Chemical, was used as    received.-   6. RX-05613, a TiO₂ functionalized with acrylate functional groups.    The coupling agent used was NZ-39.

The following is a generalized procedure for making a functionalizednanoparticle, such as RX-05613:

In a three-neck flask, is dispersed certain amount of a commercial gradenanoparticle (e.g. Al₂O₃) in powdered form in methanol by agitating forone hour. The weight ratio of methanol to the nanoparticle isapproximately 20-50:1. A certain amount of NZ-39 was dissolved inmethanol. The amount of NZ-39 is between 0.1 and 0.5% by weight of thatof the nanoparticle. With agitation, the NZ-39/methanol solution wasadded dropwise to the nanoparticle dispersion. The content in thethree-neck flask was transferred to a single neck flask. The mixture wasrefluxed in the single neck flask at 40-60° C. for approximately 2hours. The reflux temperature depends on the type of surface modifiers.Methanol was allowed to evaporate. The product was dried at 110° C. for24 hours.

-   7. Rubine Pigmet, an organic pigment obtained from Ciba-   8. TMPEOTA, trimethylolpropane ethoxy triacrylate monomer produced    by UCB.-   9. DPGDA, dipropylene glycol diacrylate monomer produced by UCB.-   10. I369, a benzophenone derivative obtained from Ciba.-   11. ITX, isopropylthioxanthone, obtained from First Chemicals.-   12. EPD, a benzophenone derivative obtained from Quantacure.-   13. BDK, a benzophenone derivative obtained from Chemfirst Fine    Chemicals.-   14. MEHQ, an inhibitor obtained from Kodak.    Test Methods-   1. Distinctness of image (DOI): The procedure is listed in    Instruments for Research and Industry Application Data Sheet    included with the Model GB 11-DOI Glow Box.-   2. Pencil Hardness was measured according to ASTM D 3363. Pencil    Scratch and Gouge Hardness were measured.-   3. 60° and 20° gloss and haze were measured on a BYK-Gardner    Haze-Gloss Meter.-   4. Methyl ether ketone (MEK) resistance was measured as MEK double    rubs in accordance with ASTM D 4752.    Melt Blending for Radiation Curable Powder Coating Systems:

3,000 g of UVECOAT 2000 was transferred to a 10-liter round-bottomflask. The resin was heated to 140-180° C. until completed melted. Thetemperature was maintained at 140-180° C. while the molten resin wasstirred. Appropriate amount of a nanoparticle of double bondfunctionality was added into the flask. The resin and nanoparticlemixture was stirred at 140-180° C. for one hour before poured into analuminum pan.

Melt Extrusion for Radiation Powder Coating Systems:

All ingredients of a radiation curable powder formulation including theresin, photoinitiator, pigment, degassing agent, and a certain type ofreactive nanoparticle were mixed in a Prism Pilot 3 High-Speed Premixer.Premix speed was 2000 RPM and total mixing time was 4 minutes. Thepremixed mixture was then extruded in a Prism 16 PC twin screw extruderat approximately 110° C. The extrudate was cooled at −30° C. for 24hours. The cooled flakes were pulverized in a Brinkmann high-speedgrinder, sieved with a 140-mesh sieve into the final powder. The powderwas applied electrostatically onto aluminum, steel or MDF substrates.The panels were cured under UV or EB lights with appropriate heating(e.g. an IR light).

Results and Discussion

Table 1 shows two UV powder formulations, U1 and U2. U1 is a standardformulation based on UVECOAT 2000 and U2 contains 4% of RX 05613, afunctionalized pigment with methacrylate functional groups attached onthe surface.

As can be seen from Table 2, appearance, surface hardness and solventresistance were all improved by the addition of RX 05613.

TABLE 1 Formulation of UV Powder Coatings Surface- Formu- ModifiedDegassing lation Resin Photoinitiator Pigment Pigments Agent No. wt % wt% Wt % wt % wt % U1 UVECOAT IRGACURE TiO₂ — 2000 819 72.1 3.5 24.0 — 0.4U2 UVECOAT IRGACURE TiO₂ TiO₂ 2000 819 RX 05613 72.1 3.5 20.0 4.0 0.4

TABLE 2 Properties of UV Curable Powder Coatings Formulation Number U1U2 Gloss 60° 95.0 99.0 20° 84.0 92.0 Haze 99.0 40.0 DOI 50 60 Pencilscratch F 3 H Hardness gauge 2 H 4 H MEK double rubs 65 140

EXAMPLE 2 Radiation Curable Ink Printing Application

NZ 33, neopentyl(diallyl)oxy trimethacryl zirconate, is a product fromKenRich Petrochemicals Inc. This coupling agent with a UV-curablemethacrylate functional group is usually employed in the surfacefunctionalization reaction of carbon black, cyan, rubine and yellowpigments. The molecular structure is represented as follows:

The functionalized pigments/dyes not only are compatible with vehicleresins, which are (meth) acrylate monomers/oligomers, but alsoco-polymerizable with these vehicle resins in UV-cure processes.

Improved compatibility of pigments/dyes with vehicle resins and alsotheir copolymerization capability render various benefits for inkprinting applications. As a result, the rheology of the ink materials,adhesion of cured inks to substrates, surface properties of cured inkssuch as surface hardness, flexibility, chemical resistance, waterresistance, corrosion resistance and weathering-ability, etc., are allimproved.

In the preparation of ink, bis phenol A epoxy diacrylate blended with amultifunctional acrylated monomer and the coupling agents were manuallyblended together and dispersed for 15 minutes using a Premier MillDispersator dispersion mill. These well-mixed blends of resins andcoupling agent were used as vehicle resins. The vehicle resins weremanually blended with the four pigments (30% black, rubine, cyan, andyellow) and then passed through the three-roll mill to make apigment-concentrate. The pigment-concentrate was passed through thethree-roll mill and tested using a Hegman grind scale after each pass.If the Hegman grind scale does not show any scratches, then the millingis terminated. If scratches are present, then the pigment-concentrate ispassed through the mill repeatedly until no scratches are observed. TheHegman grind scale is used for checking the particle size in apigment-concentrate without having to dilute the paste. The sampleconcentrate is tested as it comes from the grinding mill. It can befound that reading the gauge has been reduced to the simple task ofobserving where the coarse particles present a definite scratch in theconcentrate matrix. The Hegman scale is the most common one used in thepaint industry.

Several positive results are summarized below.

-   1. FIG. 1 shows a comparison of the ink flow of the control    (sample A) versus that of sample C. The control (see Table 4) was    the Rubine pigmented-mixture of a bis phenol A epoxy diacrylate and    a multifunctional acrylated monomer. Sample C was formulated with a    bis phenol A epoxy diacrylate+a multifunctional acrylated    monomer+Rubine pigment+NZ33 at a loading level of 0.1% (see Table    5). FIG. 2 shows a comparison of the ink flow of the control versus    sample E. Sample E was formulated with a bis phenol A epoxy    diacrylate+a multifunctional acrylated monomer+Rubine pigment+NZ33    at 0.6% (see Table 6). These figures clearly show that the addition    of the Ken Rich additives (NZ33 and NZ39) improve the flow of the    final ink.-   2. The control of cyan pigment-ink showed only a small amount of    flow off the mill. This control ink was a mixture of cyan pigments    and a bis phenol A epoxy diacrylate blended with a multifunctional    acrylated monomer. In comparison, the sample cyan pigment-ink, which    was a blend of cyan pigments, a bis phenol A epoxy diacrylate, a    multifunctional acrylated monomer, and the NZ33 coupling agent,    flowed very well off the mill. Generally, inks that demonstrate good    flow exhibit superior printing performance. In a flexographic    printing process, for example, ink transfer is directly related to    ink flow, and the transfer of ink from the anilox cells to the    printing plate is at its best when there is good flow. Good flow    usually offers high print quality. Moreover, the better the flow,    the wider the printing window, which means one can change the    printing speed without having to worry about starvation, spitting or    loss of the print quality.-   3. The most notable observation came from the milling process of the    carbon black pigment. For the control, a bis phenol A epoxy    diacrylate blended with a multifunctional acrylated monomer in black    pigment, five passes of the pigment concentrate were required to    produce a grind with no scratch. However, when the NZ33 agent was    added, no scratch was present after one pass through the mill.    Therefore, the preparation time for the two inks with the coupling    agents was drastically reduced. Since the number of passes through    the mill has been reduced, this production efficiency is increased.    The economic cost for process is significantly reduced.-   4. The gloss measurements have also demonstrated improvements in    UV-cured ink film made from the surface-functionalized pigment    formulation (see Table 3).

TABLE 3 Gloss Readings from Printed Proofs Sample 20 degrees 60 degreesControl Sample A 6.1 37.1 in FIG. 1 or 2 Sample E 7.2 40.9 in FIG. 2The formulations for inks made in the present invention are listedbelow.

TABLE 4 Control A, Red Ink Formulation Manu- Actual Weight Sample Namefacturer Type Weight % bis phenol A UCB epoxy acrylate 35.0 14.0 epoxydiacrylate blended with a multifunctional acrylated monomer Rubine Cibaorganic pigment 15.0 6.0 Pigment TMPEOTA UCB multifunctional 119.8 47.9acrylated monomer DPGDA UCB multifunctional 48.0 19.2 acrylated monomerI369 Ciba benzophenone 8.0 3.2 derivative ITX FirstIsopropylthioxanthone 8.0 3.2 Chemicals EPD Quantacure benzophenone 8.03.2 derivative BDK Chemfirst benzophenone 8.0 3.2 Fine derivativeChemicals MEHQ Kodak Inhibitor 0.2 0.1 Total 250.0 100.0

TABLE 5 Sample C, Red Ink Formulation Manu- Actual Weight Sample Namefacturer Type Weight % bis phenol A UCB epoxy acrylate 35.0 14.0 epoxydiacrylate blended with a multifunctional acrylated monomer NZ33 KenRich coupling agent 0.3 0.1 Petro- chemical Rubine Ciba organic pigment15.0 6.0 Pigment TMPEOTA UCB Multifunctional 119.8 47.9 acrylatedmonomer DPGDA UCB Multifunctional 48.0 19.2 acrylated monomer I369 Cibabenzophenone 8.0 3.2 derivative ITX First Isopropylthioxanthone 8.0 3.2Chemicals EPD Quantacure benzophenone 8.0 3.2 derivative BDK Chemfirstbenzophenone 8.0 3.2 Fine derivative Chemicals MEHQ Kodak Inhibitor 0.20.1 Total 250.3 100.0

TABLE 6 Sample E Red Ink Formulation Manu- Actual Weight Sample Namefacturer Type Weight % bis phenol A UCB epoxy acrylate 35.0 13.9 epoxydiacrylate blended with a multifunctional acrylated monomer NZ-39 KenRich coupling agent 1.5 0.6 Petro- chemicals Rubine Ciba organic pigment15.0 6.0 Pigment TMPEOTA UCB Multifunctional 119.8 47.6 monomer DPGDAUCB Multifunctional 48.0 19.1 monomer I369 Ciba benzophenone 8.0 3.2derivative ITX First Isopropylthioxanthone 8.0 3.2 Chemicals EPDQuantacure benzophenone 8.0 3.2 derivative BDK Chemfirst benzophenone8.0 3.2 Fine derivative Chemicals MEHQ Kodak Inhibitor 0.2 0.1 251.5100.0

1. An ink comprising a functionalized pigment composition produced byreacting a radiation reactive organometallic coupling agent with apigment or dye.
 2. The ink according to claim 1, wherein the couplingagent is represented by the formula:(RO)_(m)-M-(—O—X—R′—Y)_(n) where, M is a metal atom selected from thegroup consisting of Group IIa, IIIb, IVb, Vb, VIb, VIIb, VIII, Ib, IIb,and IIIa, R is C₁ to C₈ unsubstituted or substituted alkyl or hydrqgen,X is an organic functional group, R′ is an organic group which providesvan der Waals' entanglement via carbon chains, Y represents a radiationcurable functional group, m varies from 1-3 and n is 1-3.
 3. The inkaccording to claim 1 where M is Ti, Zr or Al.
 4. The ink according toclaim 1 where X is alkylene, carboxyl, sulfonyl, phenolic, phosphate,pyrophosphate or phosphite.
 5. The ink according to claim 1 where R′ isa C₂ to C₈ group.
 6. The ink according to claim 1 where Y is anunsaturated group.
 7. The ink according to claim 6 where Y is acrylate,methacrylate, epoxy or vinyl.
 8. The ink according to claim 1 furthercomprising a resin powder.
 9. The ink according to claim 1 furthercomprising a powdered resin, liquid monomer or oligomer.
 10. The inkaccording to any of claims 1 to 9 which is radiation curable.
 11. An inkcomprising a functionalized pigment composition produced by reacting acompound of formula

with a pigment or a dye.